In spinning plants it is customary to provide a number of roving frames having respective stations or spindles at which empty core sleeves are wound from sliver to form respective roving bobbins. The sliver may arrive from conventional can fields and can pass through a drafting frame before reaching the bobbins or core sleeves on which the roving is wound. When the roving bobbins are full, a bobbin replacement operation commences and, for example, a transfer unit may be displaced along the machine or a train of suspended bobbins may be displaced past the transfer unit which serves to remove the full bobbins and replace them with empty core sleeves.
The endless transport element, receiving from such a transfer unit at the roving frames, the full bobbins and delivering empty core sleeves to the roving frames, then carries the full bobbins to one or more ring-spinning frames in which the roving is spun into yarn from the roving bobbins. At the ring-spinning machines, respective transfer units can remove empty core sleeves as the roving is paid out and can replace them with full roving bobbins, the core sleeves being transferred to the transport element for return to the roving frames. The ring-spinning machines can be provided with creels or the like which hold reserve full bobbins or bobbins in use for supplying roving to those stations or for storage of empty core sleeves until the are transferred to the transporter.
It has been found, in such plants, that it is advantageous from time to time to operate with different roving qualities and for that purpose care must be taken to direct roving bobbins of a particular quality to certain ring-spinning machines and, in general, to make it possible to distinguish between roving bobbins in which the roving may be of a different quality at one point in time from another.
In DE 196 01 286, for example, (see also U.S. Pat. No. 5,732,542), each of the roving frames has a respective transfer unit which automatically removes empty core sleeves from a transport element passing by the roving frame and replaces them on that transport element with full roving bobbins. The roving frame supplies roving bobbins of a predetermined roving quality and these bobbins are carried to the ring-spinning machines. For a change in the roving quality, it is necessary to allow the transport element to carry roving bobbins of the "old" quality until all of them have been replaced by roving bobbins of the new quality in a system operating with two roving qualities.
EP 0 314 631 B1 discloses a spinning plant in which two roving frames or machines are associated with a common transporter that carries the roving bobbins of both roving frames to the ring-spinning machines associated therewith and returns the roving sleeves or cores to the roving frames. The two roving frames operate to produce different qualities of roving and the two sets of roving bobbins with their different qualities are simultaneously mounted with the transporter. When the transporter conveys more than a single roving quality, it has been necessary heretofore for service personnel or, where possible, automatic devices to differentiate between them and see that the roving bobbins or roving sleeves are withdrawn from or mounted in the transporter so that the distinction is maintained.
For this purpose, a transfer unit can be provided which removes the empty core sleeves from the transporter and feeds them into the roving frame so that they are again wound with roving bobbins. This type of transfer unit is referred to generally as a roving frame transfer system. It is based upon the condition that the transfer unit of the roving frame will only feed those roving core sleeves to the latter whose color is associated with the roving quality of the roving frame to which those core sleeves are supplied. The transfer unit can also remove full roving bobbins from the transporter and mount them in the creel of a ring-spinning machine. This type of transfer unit is referred to as a ring-spinning machine transfer unit. In this as well the transfer unit should only supply to the ring-spinning machine such roving bobbins as have a core or sleeve color associated with the roving quality to be processed in that ring-spinning machine.